alexa On the evolution of pollution from South and Southeast Asia duringthe winter-spring monsoon
Geology & Earth Science

Geology & Earth Science

Journal of Oceanography and Marine Research

Author(s): Mahesh J Phadnis, Hiram Levy II, Walter J Moxim

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The NOAA Geophysical Fluid Dynamics Laboratory three-dimensional GlobalChemical Transport Model (GFDL GCTM) is used to examine the winter-spring evolutionof pollution (fossil fuel combustion and biomass burning) from South and Southeast Asiawith special focus on the Indian Ocean region. We find that during the monsoonal winter-spring outflow, pollution over the Indian Ocean north of the ITCZ is concentrated in themaritime boundary layer and originates from both regions. South Asian emissionsdominate over the Arabian Sea and the Western Indian Ocean, while the Southeast Asianemissions have the greatest impact over the Bay of Bengal and Eastern Indian Ocean.Over these oceanic regions, CO pollution in both source regions, most of which is frombiomass burning, accounts for 30–50% of the boundary layer CO. It is transportedequatorward from South and Southeast Asian source regions and episodically lofted intothe upper troposphere by tropical convection events. This transport path has a noticableimpact (10–20%) on total CO at 300 mb and produces a maximum in a tropical belt overand north of the ITCZ. Another free troposphere transport path, primarily open toSoutheast Asian emissions, carries CO from that region out over the North Pacific andaround the Northern Hemisphere. O3production is driven by NOx, which, unlike CO,comes almost equally from biomass burning and fossil fuel combustion in this region andhas a chemical lifetime of a few days or less. The resulting NOxdistributions, whilequalitatively similar to CO, have much steeper gradients, are transported much less widely,have a much lower background, and over the Indian and Pacific Oceans, are stronglydominated by pollution. O3resulting from these anthropogenic sources generally exhibitspatterns similar to those found for CO and NOx. Pollution accounts for 20–50% of thenear-surface O3and 5–10% of the O3in the upper troposphere. South and SoutheastAsian emissions only produce 25% of the boundary layer O3in the continental sourceregions. The maximum impact of the emissions occurs over the Indian Ocean (25–40%)with comparable contributions from O3produced in the continental emission regions andO3produced over the ocean by transported precursors. Convective lifting of thetransported pollution O3supplies  10% of the O3in the tropical upper troposphere. Whileboth emission regions have modest impacts on O3(5–10%) outside of the Indian Oceanregion, Southeast Asian pollution impacts free troposphere O3in a midlatitude belt acrossthe North Pacific, similar to NOx.

This article was published in JOURNAL OF GEOPHYSICAL RESEARCH and referenced in Journal of Oceanography and Marine Research

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